Qualla: Large Helical Device

Large Helical Device: Introduction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit Erhan Önal, CC BY-SA 3.0. In the quiet city of Toki, surrounded by the ceramic workshops and forested hills of Gifu Prefecture, sits a machine designed to recreate the physics of a star. The Large Helical Device is not a tokamak -- the doughnut-shaped reactor that dominates most fusion headlines -- but a stellarator, a fundamentally different approach to containing superheated plasma using twisted magnetic fields generated entirely by external coils. As the world's second-largest superconducting stellarator after Germany's Wendelstein 7-X, the LHD represents Japan's distinctive contribution to the global quest for fusion energy. And in 2017, it achieved something remarkable: an ion temperature of 120 million degrees Celsius, one of the threshold conditions for a working fusion reactor.

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Image: Erhan Önal | CC BY-SA 3.0

Large Helical Device: The Twisted Path to Fusion

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit National Institute for Fusion Science, CC BY-SA 4.0. Most people who have heard of fusion reactors think of tokamaks -- the Russian-invented design that uses a combination of external magnets and electrical current running through the plasma itself to create a confining magnetic field. Stellarators take a radically different approa...

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Image: National Institute for Fusion Science | CC BY-SA 4.0

Large Helical Device: Eight Years of Construction

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit National Institute for Fusion Science, CC BY-SA 4.0. The LHD's design was finalized in 1987, and construction began in 1990 at the National Institute for Fusion Science campus in Toki. Eight years of precision engineering followed, assembling superconducting coils cooled to near absolute zero, a vacuum vessel to hold the plasma, an...

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Image: National Institute for Fusion Science | CC BY-SA 4.0

Large Helical Device: Breaking Stellarator Records

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit National Institute for Fusion Science, CC BY-SA 4.0. The LHD holds all major performance records for stellarators. In 2005, it maintained a stable plasma for 3,900 seconds -- over an hour of continuous operation, demonstrating the steady-state capability that gives stellarators their theoretical edge over pulsed tokamaks. A new hel...

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Image: National Institute for Fusion Science | CC BY-SA 4.0

Large Helical Device: A Star in the Countryside

Mon, 16 Feb 2026 00:00:00 GMT

Photo credit National Institute for Fusion Science, CC BY-SA 4.0. There is something striking about the contrast between the LHD's surroundings and its mission. Toki is a small city of about 60,000 people, better known for Mino ware pottery than particle physics. The forested hills of eastern Gifu Prefecture give no hint that behind the walls o...

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Image: National Institute for Fusion Science | CC BY-SA 4.0